Methods of making medical devices

ABSTRACT

A method of making a stent includes providing a tubular member having a first layer, the first layer and the tubular member having different compositions, removing a portion of the tubular member, and removing a portion of the first layer from the tubular member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation or application of and claims priorityto U.S. application Ser. No. 10/185,837, filed on Jun. 27, 2002.

TECHNICAL FIELD

The invention relates to methods of making medical devices, such as, forexample, endoprostheses.

BACKGROUND

The body includes various passageways such as arteries, other bloodvessels, and other body lumens. These passageways sometimes becomeoccluded or weakened. For example, the passageways can be occluded by atumor, restricted by plaque, or weakened by an aneurysm. When thisoccurs, the passageway can be reopened or reinforced, or even replaced,with a medical endoprosthesis. An endoprosthesis is typically a tubularmember that is placed in a lumen in the body. Examples of endoprosthesisinclude stents and covered stents, sometimes called “stent-grafts”.

An endoprosthesis can be delivered inside the body by a catheter thatsupports the endoprosthesis in a compacted or reduced-size form as theendoprosthesis is transported to a desired site. Upon reaching the site,the endoprosthesis is expanded, for example, so that it can contact thewalls of the lumen.

The expansion mechanism may include forcing the endoprosthesis to expandradially.

For example, the expansion mechanism can include the catheter carrying aballoon, which carries the endoprosthesis. The balloon can be inflatedto deform and to fix the expanded endoprosthesis at a predeterminedposition in contact with the lumen wall. The balloon can then bedeflated, and the catheter removed.

In another delivery technique, the endoprosthesis is formed of anelastic material that can be reversibly compacted and expanded. Duringintroduction into the body, the endoprosthesis is restrained in acompacted condition. Upon reaching the desired implantation site, therestraint is removed, for example, by retracting a restraining devicesuch as an outer sheath, enabling the endoprosthesis to self-expand byits own internal elastic restoring force.

One method of making a stent includes laser cutting a tube of stentmaterial to define the structure of the stent. Laser cutting, however,can form recast material, which is material from the tube that hasmelted, oxidized, and solidified on laser-cut surfaces. The recastmaterial can make a stent more susceptible to failure (e.g., cracking orfracture) during manufacturing or in use. Accordingly, sometimes, therecast material is removed, e.g., by chemical milling and/orelectropolishing, after laser cutting. To compensate for loss ofmaterial during the removal step(s), the metal tube can be madeoversized, which can be wasteful and costly, particularly if the tubeincludes precious metals. The removal step(s) may also include usingpotent and/or hazardous chemicals.

SUMMARY

The invention relates to methods of making medical devices, such as, forexample, endoprostheses.

The invention features a method of manufacturing an endoprosthesis, suchas a stent, that includes using sacrificial material that covers one ormore portions of a tube of stent material. During manufacturing,particularly during removal of recast material, the sacrificial materialprotects the stent material from material loss. As a result, althoughthe tube of stent material can be formed oversized, the tube does notneed to be formed oversized, thereby reducing the amount of stentmaterial used. When the stent material includes precious materials, suchas gold or platinum, reducing the amount of stent material reduces cost.The sacrificial material may also be capable of reacting with the stentmaterial to form a product, such as an alloy, that is relatively easy toremove, e.g., compared to the pure stent material. As a result, lesshazardous chemicals may be used during recast material removal.

In one aspect, the invention features a method of making a stent. Themethod includes providing a tubular member having a first layer, thefirst layer and the tubular member having different compositions,removing a portion of the tubular member, and removing a portion of thefirst layer from the tubular member.

In another aspect, the invention features a method of making a stenthaving struts including providing a tubular member having a first layer,the first layer and the tubular member having different compositions,removing a portion of the tubular member to form the struts and aportion of the first layer, and removing a portion of the first layerfrom the tubular member to provide the stent.

In another aspect, the invention features a method of making a stentincluding providing a member having a first layer, the first layer andthe member having different compositions, removing a portion of themember to define an opening through the member, removing the first layerfrom the member, and forming the member into the stent. The member mayhave opposing edges, and the stent may be formed by connecting theedges. The stent can be formed by forming the member into a tube. Themember can be tubular.

Embodiments of the aspects of the invention may include one or more ofthe following features. The tubular member and the first layer includemetals. The method further includes finishing the tubular member intothe stent, e.g., by electropolishing. A portion of the first layer isremoved with the portion of the tubular member. The entire first layeris removed from the tubular member. An entire surface portion of thefirst layer is removed from the tubular member.

The first layer can be directly on the tubular member. The first layercan be on only a portion of the tubular member or on substantially anentire surface of the tubular member. The first layer can be on an innersurface and/or on an outer surface of the tubular member.

In some embodiments, the tubular member has a second layer, and thefirst and second layers are on opposing surfaces of the tubular member.The method may include removing a portion of the tubular member and thefirst and second layers, and removing the first and second layers fromthe tubular member.

The tubular member can be provided by co-drawing a first member thatforms the tubular member and a second member that forms the first layeron an inner surface of the tubular member. The tubular member can beprovided by co-drawing a first member that forms the tubular member anda second member that forms the first layer on an outer surface of thetubular member.

The method can include forming the first layer on the tubular member.The first layer may include a metal and may be formed by a processselected from a group consisting of electrodeposition and vapordeposition of the metal.

The stent may include struts, and the removing of the portion of thetubular member may include forming the struts.

The portion of the tubular member may be removed by a laser, bydissolving the first layer, by melting the first layer, and/or bymechanically removing the first layer.

The tubular member may include a material selected from a groupconsisting of platinum, gold, palladium, rhenium, tantalum, tungsten,molybdenum, rhenium, nickel, cobalt, stainless steel, Nitinol, andalloys thereof. The first layer may include a material selected from agroup consisting of steel, cadmium, lead, magnesium, tin, zinc,titanium, stainless steel, and aluminum.

The method may include forming a drug-releasing layer on the stent.

In another aspect, the invention features a stent, made according to themethods described herein.

Other aspects, features, and advantages of the invention will beapparent from the description of the preferred embodiments thereof andfrom the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a method of making a stent; and

FIG. 2 is a schematic diagram of a method of making a stent.

DETAILED DESCRIPTION

Referring to FIG. 1, a method 10 of making a stent 12 is shown. Method10 generally includes providing a tubular member 14 that ultimatelybecomes stent 12, and forming an inner layer 16 and an outer layer 18 onthe tubular member. Tubular member 14 is made of a stent material, e.g.,platinum, and layers 16 and 18 can be made of, e.g., carbon steel.Portions of tubular member 14 and layers 16 and 18 are then removed,e.g., by laser cutting, to form openings 20 and struts 22 of stent 12.Subsequently, layers 16 and 18 are removed from tubular member 14 toyield stent 12.

Layers 16 and 18 serve as sacrificial layers that are ultimately removedat the end of method 10. Here, rather than starting with an oversizedtubular member to compensate for loss of material that may occur duringremoval of recast material, a relatively smaller tubular member 14 canbe used with layers 16 and 18. For example, tubular member 14 and layers16 and 18 can have a total dimension similar to that of an oversizedtubular member. During removal of recast material, layers 16 and 18 aresacrificed, reducing the amount of tubular member 14 that is affected byrecast material removal. In embodiments in which tubular member 14includes precious metals, such as platinum, using layers 16 and 18 canreduce cost and waste. In other embodiments, an oversized tubular membercan be used.

Furthermore, without wishing to be bound by theory, it is believed thatduring laser cutting, portions of layers 16 and 18 can pave cut surfacesof tubular member 14 and/or react with the tubular member, e.g., at thecut surfaces to form products such as alloys. Some reaction products canbe more easily removed, e.g., by chemical etching, than a pure stentmaterial, such as an acid-resistant precious metal. As a result, in someembodiments, less hazardous materials may be used in the post-lasercutting removal step(s). Some reaction products may also protect the cutsurfaces by making the surfaces less susceptible to oxidation.

Moreover, since tubular member 14 can be relatively small, smalleringots can be used to form the tubular member. Smaller ingots can beformed with relatively high yield rates, i.e., low waste, and relativelyhigh quality control. Also, during manufacturing, layers 16 and 18 canprotect tubular member 14, e.g., by lowering the oxidation of thetubular member by the environment and/or by reducing contamination ofthe tubular member, e.g., from machining equipment. Consequently,manufacturing steps, such as annealing to enhance the physicalproperties to tubular member 14, e.g., ductility, may be performedwithout certain handling equipment, such as vacuum or inert gasannealing chambers, which can further reduce cost and inconvenience.

Tubular member 14 can be made of any material that can be used in astent. The material is preferably biocompatible. Examples of stentmaterials include noble metals, such as platinum, gold, and palladium,refractory metals, such as tantalum, tungsten, molybdenum and rhenium,and alloys thereof. Other examples of stent materials include stainlesssteels, stainless steels alloyed with noble and/or refractory metals,nickel-based alloys (e.g., those that contained Pt, Au, and/or Ta),iron-based alloys (e.g., those that contained Pt, Au, and/or Ta),cobalt-based alloys (e.g., those that contained Pt, Au, and/or Ta), andNitinol. Tubular member 14 can be made, for example, by extrusion anddrawing, or by boring a solid billet of stent material. As an example,tubular member 14 can be made from a casted two-inch diameter ingot thatis rough machined, rolled, forged, and/or extruded to a 1.5-inchdiameter by six-inch long billet. A one-inch diameter bore can be formedin the billet by upset forging and/or electrical discharge machining(EDM). As described below, tubular member 14 can have dimensions thatare near final stent size or greater.

Tubular member 14 can be annealed after it is formed. In general,annealing can be performed after any step (such as forging, extrusion,or drawing) that has reduced the formability (e.g., ductility) oftubular member 14. Annealing tubular member 14 can increase theformability of the tubular member to a level sufficient for furtherprocessing (e.g., without the tubular member cracking or fracturing).

Layers 16 and 18 can include any material that can be formed on tubularmember 14 and subsequently removed. Examples of materials for layers 16and 18 are those that are relatively convenient to handle, relativelyconvenient to form on tubular member 14, relatively easy to remove,e.g., chemically, and/or relatively inexpensive. Preferably, thematerials for layers 16 and 18 can react with the stent material to forma product that is convenient or easy to remove. Layers 16 and 18 canhave similar melting points as that of tubular member 14 or higher,e.g., so that the layers can be annealed with the tubular member, i.e.,the layers do not melt or degrade during heating. In some embodiments,materials for layers 16 and 18 have relatively low melting points, e.g.,so that the layers can be removed by heating. Examples of materials forlayers 16 and 18 include metallic materials, such as carbon steel,cadmium, lead, magnesium, tin, zinc, titanium, stainless steel (e.g.,304L or 316L stainless steel), and aluminum. The thickness of each layer16 or 18 can be about 0.25-2 times, e.g., 0.5-1 time, the wall thicknessof tubular member 14. Layers 16 and 18 can have the same or differentcompositions.

Numerous methods can be used to form layers 16 and 18 on tubular member14. For example, a tubular member 14 that is larger than final stentsize can be sandwiched between layers 16 and 18 by placing a tightfitting tube (e.g., a steel tube) around the tubular member, and anothertight fitting tube (e.g., a hollow or solid die or a mandrel) in thetubular member. Tubular member 14 and the sandwiching tubes can then beco-drawn, e.g., until the tubular member is near final stent size. As anexample, a 1.5-inch diameter tubular member having a one-inch diameterbore can be placed into an outer steel tube having a 1.5193-inch O.D.and a 1.5-inch I.D. An inner steel tube having a one-inch O.D. and a0.9745-inch I.D. can be placed in the tubular member. The tubular memberand sandwiching steel tubes can be drawn until the O.D. and the I.D. ofthe tubular member are reduced to about 0.07 and 0.06 inch,respectively. A 0.0002-inch thick steel layer can be on each surface ofthe tubular member after drawing.

In other embodiments, tubular member 14 can be formed, e.g., drawn, tonear final stent size, and layers 16 and 18 are subsequently formed onthe tubular member. Methods of forming layers 16 and 18 include, forexample, electrodeposition, spraying, e.g., plasma spraying, dipping inmolten material, e.g., galvanizing, chemical vapor deposition, andphysical vapor deposition.

After layers 16 and 18 are formed on tubular member 14, portions of thelayers and tubular member are removed to form the structure (e.g.,openings 20 and struts 22) of stent 12. The portions can be removed bylaser cutting, as described in U.S. Pat. No. 5,780,807, herebyincorporated by reference in its entirety. In certain embodiments,during laser cutting, a liquid carrier, such as a solvent or an oil, isflowed through tubular member 14 (arrow A). The carrier can preventdross formed on one portion of tubular member 14 from re-depositing onanother portion, and/or reduce formation of recast material on thetubular member. Other methods of removing portions of tubular member 14and layers 16 and 18 can be used, such as mechanical machining (e.g.,micro-machining), electrical discharge machining (EDM), and photoetching(e.g., acid photoetching).

After the structure of stent 12 is formed, layers 16 and 18 are removedto yield stent 12. Layers 16 and 18 can be dissolved, e.g., by immersionin an acid such as nitric acid, which can also remove certain recastmaterial formed on tubular member 14 (now formed into stent 12).Alternatively or in addition, layers 16 and 18 can be mechanicallyremoved, e.g., by grinding, melting, e.g., for layers havingsufficiently low melting points, and/or subliming.

Stent 12 can then be finished, e.g., electropolished to a smooth finish,according to conventional methods. As an example, about 0.0001 inch ofthe stent material can be removed from each surface by chemical millingand electropolishing to yield a stent having a 0.0695-inch O.D. and a0.0605-inch I.D. Stent 12 can then be annealed.

Stent 12 can be used, e.g., delivered and expanded, according toconventional methods.

Generally, stent 12 can be a conventional stent, e.g., balloonexpandable, self-expandable, or a combination of both. Stent 12 can alsobe a part of a stent-graft. The stent-graft can be a stent attached to abiocompatible, non-porous or semi-porous polymer matrix made ofpolytetrafluoroethylene (PTFE), expanded PTFE, polyethylene, urethane,or polypropylene. Stent 12 can include a releasable therapeutic agent ora pharmaceutically active compound, such as described in U.S. Pat. No.5,674,242, and commonly-assigned U.S. Ser. No. 09/895,415, filed Jul. 2,2001, all hereby incorporated by reference. The therapeutic agents orpharmaceutically active compounds can include, for example,anti-thrombogenic agents, antioxidants, anti-inflammatory agents,anesthetic agents, anti-coagulants, and antibiotics. Examples of stent12 are described in U.S. Pat. Nos. 5,725,570 and 5,234,457, all herebyincorporated by reference.

OTHER EMBODIMENTS

In other embodiments, a non-tubular member can be initially used to forma stent. Referring to FIG. 2, a method 100 of forming a stent 112 beginswith using a non-tubular member 114 (here, a sheet). Member 114 can besimilar in composition to tubular member 14 described above. Member 114can be formed, for example, by forging, rolling, and/or extrusion. Next,sacrificial layers 116 and 118, which are similar to layers 16 and 18,are formed on member 114, as generally described above. Portions ofmember 114 and layers 116 and 118 are then removed, e.g., by lasercutting, to form openings 120 and struts 112 of stent 112. Layers 116and 118 are then removed, e.g., by chemical etching, to leave member114. Member 114 can be formed into stent 112 by connecting opposingedges 124 and 126, e.g., by welding. Stent 112 can be finished asdescribed above. In some embodiments, opposing edges of member 114 andlayers 116 and 118 can be connected together to form a tube prior tolaser cutting.

As an example, a casted and rough machined two-inch diameter by six inchlong ingot of stent material can be upset forged and extruded down to abar about one inch thick by one inch wide by 18.85 inch long for plateand strip rolling. The bar can be placed within a tight fitting steelcontainer with a wall thickness of 0.0435 inch. The steel-covered barcan be subjected to plate and strip rolling operations until thethickness of the stent material is 0.0046 inch and the total sandwichthickness is 0.0050 inch. A 0.0002-inch thick steel layer may be on eachsurface of the stent material. A stent tubing can be formed by rollingand laser welding of the steel-sandwiched stent material. The weldedtubing can be laser machined to form the structure of the stent, and themachined stent can be immersed in a nitric acid solution to dissolve thesteel from the surfaces of the stent and the recast material on the cutsurfaces. The stent can then be electropolished to a smooth surfacefinish, with 0.00005 inch of stent material removed from each surfacefrom chemical milling and electropolishing.

In some embodiments, one or more of sacrificial layers 16, 18, 116, or118 cover selected portions of member 14 or 114. For example, thesacrificial layers may cover only portions of member 14 or 114 thatbecome the struts of the stent, i.e., portions of the member 14 or 114that are removed to form the openings of the stent are not covered bythe sacrificial layers. Selective coverage of members 14 or 114 can beperformed, e.g., by masking techniques.

In certain embodiments, layers 16, 18, 116, or 118 are formed on thestent material ingot to protect the stent material during billet or tubeforming. The melting points of layers 16, 18, 116, or 118 may be about50% of the melting point of stent material or more.

In other embodiments, only one layer (e.g., layer 16, 18, 116, or 118)is formed on the member (e.g., member 14 or 114) that ultimately becomesthe stent. As an example, a two-inch diameter ingot of stent materialcan be rough machined, rolled, forged, and/or extruded down to a1.5-inch diameter by six-inch long billet. A one-inch diameter hole canbe made in the billet by upset forging or electrical dischargemachining. The billet can be placed inside a tight fitting steel tubewith a 1.5-inch diameter I.D. and a wall thickness of 0.0045 inch. Thesteel covered billet can be subjected to tube drawing operations untilthe O.D. and I.D. are 0.0700 inch and 0.0602 inch, respectively. A0.0001-inch thick steel layer may remain on the outer surface of thestent material tubing. Laser cutting of the stent struts can beperformed. The machined tube can be immersed in a nitric acid solutionto dissolve the steel from the outer surface of the tube and the steelrecast material on the cut surfaces. The stent can then be chemicalmilled and electropolished to a smooth surface finish (e.g., 0.0003 inchof stent material removed from each surface). The finished stentdimensions can be 0.0695 inch O.D. and 0.0605 inch I.D.

In some embodiments, layers 16, 18, 116 and/or 118 are not completelyremoved from tubular member 14 or member 114 because, for example, thelayer(s) can enhance the function or performance of the stent. Forexample, a thin film of titanium or 316 L stainless steel may remain onmember 14 or 114 to enhance biocompatibility of a gold or tungstenmember 14 or 114. An entire surface portion of layers 16, 18, 116 and/or118 can be removed, leaving the layers reduced in thickness but stillremaining on member 14 or 114.

More than one sacrificial layer can be formed on each side of member 14or 114. A sacrificial layer may be in direct contact with member 14 or114, or there may be intermediate layers between the sacrificial layerand member 14 or 114.

Other embodiments are within the claims.

1. A method of making a stent, the method comprising: providing atubular member having a first layer, the first layer and the tubularmember having different compositions; removing a portion of the tubularmember; and removing a portion of the first layer from the tubularmember.
 2. The method of claim 1, wherein the tubular member and thefirst layer comprise metals.
 3. The method of claim 1, furthercomprising finishing the tubular member into the stent.
 4. The method ofclaim 3, wherein the tubular member is finished by electropolishing. 5.The method of claim 1, wherein the first layer is directly on thetubular member.
 6. The method of claim 1, wherein the first layer is ononly a portion of the tubular member.
 7. The method of claim 1, whereinthe first layer is on substantially an entire surface of the tubularmember.
 8. The method of claim 1, wherein the first layer is on an innersurface of the tubular member.
 9. The method of claim 1, wherein thefirst layer is on an outer surface of the tubular member.
 10. The methodof claim 1, wherein a portion of the first layer is removed with theportion of the tubular member.
 11. The method of claim 1, wherein thetubular member has a second layer, the first and second layers being onopposing surfaces of the tubular member, and the method comprisesremoving a portion of the tubular member and the first and secondlayers, and removing the first and second layers from the tubularmember.
 12. The method of claim 1, wherein the tubular member isprovided by co-drawing a first member that forms the tubular member anda second member that forms the first layer on an inner surface of thetubular member.
 13. The method of claim 1, wherein the tubular member isprovided by co-drawing a first member that forms the tubular member anda second member that forms the first layer on an outer surface of thetubular member.
 14. The method of claim 1, further comprising formingthe first layer on the tubular member.
 15. The method of claim 14,wherein the first layer comprises a metal and is formed by a processselected from a group consisting of electrodeposition and vapordeposition of the metal.
 16. The method of claim 1, wherein the stentcomprises struts, and the removing of the portion of the tubular membercomprises forming the struts.
 17. The method of claim 1, wherein theportion of the tubular member is removed by a laser.
 18. The method ofclaim 1, wherein the first layer is removed by dissolving the firstlayer.
 19. The method of claim 1, wherein the first layer is removed bymelting the first layer.
 20. The method of claim 1, wherein the firstlayer is removed by mechanically removing the first layer.
 21. Themethod of claim 1, wherein the tubular member comprises a materialselected from a group consisting of platinum, gold, palladium, rhenium,tantalum, tungsten, molybdenum, rhenium, nickel, cobalt, stainlesssteel, Nitinol, and alloys thereof.
 22. The method of claim 1, whereinthe tubular member comprises a material selected from a group consistingof platinum, gold, and tantalum.
 23. The method of claim 1, wherein thefirst layer comprises a material selected from a group consisting ofsteel, cadmium, lead, magnesium,.tin, zinc, titanium, stainless steel,and aluminum.
 24. The method of claim 1, wherein the first layercomprises a steel.
 25. The method of claim 1, further comprising forminga drug-releasing layer on the stent.
 26. The method of claim 1, whereinthe entire first layer is removed from the tubular member.
 27. Themethod of claim 1, wherein an entire surface portion of the first layeris removed from the tubular member.
 28. A stent, made according to themethod of claim
 1. 29. A method of making a stent, the methodcomprising: providing a member having a first layer, the first layer andthe member having different compositions; removing a portion of themember to define an opening through the member; removing a portion ofthe first layer from the member; and forming the member into the stent.30. The method of claim 29, wherein the member has opposing edges, andthe stent is formed by connecting the edges.
 31. The method of claim 29,wherein the stent is formed by forming the member into a tube.
 32. Themethod of claim 29, wherein the member is tubular.
 33. The method ofclaim 29, wherein the member and the first layer comprise metals. 34.The method of claim 29, further comprising finishing the member into thestent.
 35. The method of claim 34, wherein the tubular member isfinished by electropolishing.
 36. The method of claim 29, wherein thefirst layer is directly on the member.
 37. The method of claim 29,wherein the first layer is on only a portion of the member.
 38. Themethod of claim 29, wherein the first layer is on substantially anentire surface of the member.
 39. The method of claim 29, wherein aportion of the first layer is removed with the portion of the member.40. The method of claim 29, wherein the member has a second layer, thefirst and second layers being on opposing surfaces of the member, andthe method comprises removing a portion of the member and the first andsecond layers, and removing the first and second layers from the member.41. The method of claim 29, further comprising forming the first layeron the member.
 42. The method of claim 41, wherein the first layercomprises a metal and is formed by a process selected from a groupconsisting of electrodeposition and vapor deposition of the metal. 43.The method of claim 29, wherein the stent comprises struts, and theremoving of the portion of the member comprises forming the struts. 44.The method of claim 29, wherein the portion of the member is removed bya laser.
 45. The method of claim 29, wherein the first layer is removedby dissolving the first layer.
 46. The method of claim 29, wherein thefirst layer is removed by melting the first layer.
 47. The method ofclaim 29, wherein the first layer is removed by mechanically removingthe first layer.
 48. The method of claim 29, wherein the membercomprises a material selected from a group consisting of platinum, gold,palladium, rhenium, tantalum, tungsten, molybdenum, rhenium, nickel,cobalt, stainless steel, Nitinol, and alloys thereof.
 49. The method ofclaim 29, wherein the member comprises a material selected from a groupconsisting of platinum, gold, and tantalum.
 50. The method of claim 29,wherein the first layer comprises a material selected from a groupconsisting of steel, cadmium, lead, magnesium, tin, zinc, and aluminum.51. The method of claim 29, wherein the first layer comprises a steel.52. The method of claim 29, further comprising forming a drug-releasinglayer on the stent.
 53. A stent, made according to the method ofclaim
 1. 54. The method of claim 29, wherein the entire first layer isremoved from the member.
 55. The method of claim 29, wherein an entiresurface portion of the first layer is removed from the member.
 56. Amethod of making a stent having struts, the method comprising: providinga tubular member having a first layer, the first layer and the tubularmember having different compositions; removing a portion of the tubularmember to form the struts and a portion of the first layer; and removingthe first layer from the tubular member to provide the stent.
 57. Themethod of claim 56, wherein the first layer is on an inner surface ofthe tubular member.
 58. The method of claim 56, wherein the first layeris on an outer surface of the tubular member.
 59. The method of claim56, wherein the tubular member comprises a second layer on the tubularmember, the first and second layers being on opposing surfaces of thetubular member.
 60. The method of claim 56, wherein the first layer ison an entire surface of the tubular member.
 61. The method of claim 56,further comprising forming a drug-releasing layer on the stent.